A focused ion beam apparatus is known as an apparatus for processing and observing a fine sample such as a semiconductor device. A FIB-SEM composite apparatus is known as an apparatus for observing a sample under processing by a focused ion beam through a scanning electron microscope in real time.
In the FIB-SEM composite apparatus, in general, an FIB column and an SEM column are arranged so that an angle formed by an irradiation axis of the FIB column and an irradiation axis of the SEM column is approximately between 50 degrees to 60 degrees. With this arrangement, the same region of a sample can be observed by FIB and SEM.
Due to the reduction in device dimensions in recent years, it has been required to observe a cross-section processed by FIB with a high resolution by SEM. As an apparatus for realizing fine processing by FIB and high resolution observation by SEM, there has been proposed a composite charged particle beam apparatus in which the FIB column and the SEM column are arranged perpendicularly (see JP-A-H06-231720).
In this apparatus, the cross-section processed by FIB can be observed by SEM from a direction perpendicular thereto. In SEM observation, in general, when an observation surface of a sample is observed from a direction perpendicular thereto, observation can be performed with a high resolution. According to the apparatus described in JP-A-H06-231720, the cross-section processed by FIB is irradiated with an electron beam simultaneously from the direction perpendicular to the cross-section, and hence, SEM observation can be performed with a high resolution.
As an observation preparation for high resolution SEM observation, it is necessary to adjust a position of the sample so that the observation surface of the sample is perpendicular to an irradiation axis of the electron beam. As a position adjusting method, for example, there is known a method of measuring heights of the sample at a plurality of points in the observation surface, calculating a tilt of the observation surface based on the measurement results, and tilting the sample so as to correct the tilt of the observation surface. In this case, the heights of the sample are measured by tilting the sample and measuring the eucentric height at each measurement point in the observation surface.
According to this method, however, the sample needs to be moved and tilted many times, and hence, observation preparation time becomes long. Further, a tip of a beam column, a detector, and other components are arranged close together in the vicinity of the sample at the intersection of an ion beam and an electron beam, and hence, the tilt angle of the sample cannot be increased, and thus, the eucentric height cannot be adjusted with high accuracy. Thus, it has been difficult to measure the sample height with high accuracy.